Neodymium-iron-boron magnets find wide application due to their excellent magnetic properties, viz. a very high coercivity, a high remanence and a very high maximum energy product. They are increasingly used in motors, generators, measuring and control devices, telecommunications, acoustic devices and magneto-mechanical applications. They also find applications in aerospace components, instrumentation, medical diagnosis and treatment.
In conventional methods of production of neodymium-iron-boron magnets, the individual elements such as neodymium, iron and boron or ferroboron are melted crushed and milled to micron size, compacted under magnetic field and then sintered. This known process is energy intensive as well as costly. The rare earth metal, neodymium which is the raw material for the process is very expensive because of the difficulties in the separation of neodymium oxide/salt from the mixture of rare earth oxides/salts and the reduction of neodymium oxide/salt into metal. In another known process wherein metallothermic reduction diffusion is involved, neodymium chloride/fluoride or oxide, iron and boron or ferroboron are reacted with calcium in the presence of hydrogen to get neodymium-iron-boron alloy along with calcium oxide and unreacted calcium. This is further reacted with water/moist nitrogen to remove calcium and then leached with acetic acid to remove calcium oxide. This process also requires considerable amount of energy input in preparation of alloy during reduction with calcium at high temperature in the range of 1000 to 1200° C.
Indian patent application No. 374/Del/94 dated 31.03.94, discloses a process for the production of nano sized neodymium-iron-boron permanent magnet alloy powder. The process employs neodymium oxide/salt, iron salt and borohydride for making neodymium-iron-boron alloy powder with particle size in the range of 20-100 nm (nm: nanometer). The use of borohydride as a reductant helps in the reduction of neodymium and iron salt to their metallic state and formation of the compound is accomplish through suitable heat treatment. The as produced powder being highly pyrophoric needs specific surface treatment to stabilize it. However, this coating some times leads to problems when the powder is subjected to further heat treatment.
Prior art methods also require several steps for the manufacture of neodymium-iron-boron permanent magnet alloy powder and are time consuming. Neodymium-iron-boron alloy with a characteristic microstructure and phase as required for the production of permanent magnet which are not achieved by the prior art processes enumerated above. Prior art processes also require high temperature treatment thereby increasing the energy costs in the manufacture of neodymium-iron-boron alloy.